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New techniques for integral field spectroscopy - II. Performance of the GNIRS IFU
We present results on the performance of the integral field spectroscopy(IFS) capability of the Gemini Near-Infrared Spectrograph installed onthe Gemini-North telescope. This makes use of the innovative AdvancedImage Slicer optical concept described in Paper 1 and uses newdevelopments in diamond-machining to produce its complex micro-optics.The system delivers near-optimal performance for IFS in a small packagethat can be adapted to work with a wide range of spectrographs.In this paper, we present results of extensive tests carried out on thetelescope to verify the measurements of throughput, image quality andscattered light obtained in the laboratory and characterize theinstrument's geometry and spectroscopic performance. This shows that theperformance model, when fed with results of the component surfacemetrology, provides a good match to the throughput of the integral fieldunit measured on the telescope between 1 and 2.5 μm (65 and 90 percent, respectively). At longer wavelengths, the throughput exceeds 90per cent and the way that the design handles diffraction means that itsperformance can actually exceed that of the spectrograph alone with aslit of equivalent width.We also present examples of data obtained during commissioning andsystem verification and compare this with data obtained in other ways,to verify the system performance in recovering astrophysical data.Finally, we review the performance and its relevance to futureterrestrial and space observatories, in particular for large-scalemultiple-IFS applications. We make the case that our design is of greatrelevance to instrumentation for Extremely Large Telescopes. We showthat the throughput can be improved further by techniques to improve thequality of the optical surfaces.
| L- and M-band imaging observations of the Galactic Center region
In this paper we present near-infrared H-, K-, L- and M-band photometryof the Galactic Center from images obtained at the ESO VLT in May andAugust 2002, using the NAOS/CONICA (H and K) and the ISAAC (L and M)instruments. The large field of view (70´´ ×70´´) of the ISAAC instrument and the large number ofsources identified (L-M data for a total of 541 sources) allows us toinvestigate their colors, infrared excesses and the extended dustemission. Our new L-band magnitude calibration reveals an importantoffset to the traditionally used “standard” calibrations,which we attribute to the use of the variable star IRS 7 as a fluxcalibrator. Together with new results on the extinction towards theGalactic Center [CITE], our magnitude calibration results in stellarcolor properties expected from standard stars and removes any necessityto modify the K-band extinction. The large number of sources for whichwe have obtained L-M colors allows us to measure the M-band extinctionto AM = (0.056 ± 0.006)A_V, i.e. A_M≈ A_L, aconsiderably higher value than what has so far been assumed. L-M colordata has not been investigated previously, due to lack of useful M-banddata. We find that this color is a useful diagnostic tool for thepreliminary identification of stellar types, since hot and cool starsshow a fairly clear L-M color separation, with average L-M colors of0.46 ± 0.17 for emission-line stars and -0.05 ± 0.27 forcool red giants/AGB stars. This is especially important if visual colorsare not available, as in the Galactic Center. For one of the mostprominent dust embedded sources, IRS 3, we find extended L- and M-bandcontinuum emission with a characteristic bow-shock shape. An explanationfor this unusual appearance is that IRS 3 consists of a massive, hot,young mass-losing star surrounded by an optically thick, extended dustshell, which is pushed northwest by wind from the direction of the IRS16 cluster and Sgr A*.Tables 1 and 2 are only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/433/117.Based on observing run 69.B-0101(A) at the Very Large Telescope (VLT) ofthe European Southern Observatory (ESO) on Paranal in Chile.
| Formation scenarios for the young stellar associations between galactic longitudes l = 280degr - 360degr
We investigate the spatial distribution, the space velocities and agedistribution of the pre-main sequence (PMS) stars belonging toOphiuchus, Lupus and Chamaeleon star-forming regions (SFRs), and of theyoung early-type star members of the Scorpius-Centaurus OB association.These young stellar associations extend over the galactic longituderange from 280degr to 360degr , and are at a distance interval ofaround 100 and 200 pc. This study is based on a compilation ofdistances, proper motions and radial velocities from the literature forthe kinematic properties, and of basic stellar data for the constructionof Hertzsprung-Russel diagrams. Although there was no well-known OBassociation in Chamaeleon, the distances and the proper motions of agroup of 21 B- and A-type stars, taken from the Hipparcos Catalogue,lead us to propose that they form a young association. We show that theyoung early-type stars of the OB associations and the PMS stars of theSFRs follow a similar spatial distribution, i.e., there is no separationbetween the low and the high-mass young stars. We find no difference inthe kinematics nor in the ages of these two populations studied.Considering not only the stars selected by kinematic criteria but thewhole sample of young early-type stars, the scattering of their propermotions is similar to that of the PMS stars and all the young starsexhibit a common direction of motion. The space velocities of theHipparcos PMS stars of each SFR are compatible with the mean values ofthe OB associations. The PMS stars in each SFR span a wide range of ages(from 1 to 20 Myr). The ages of the OB subgroups are 8-10 Myr for UpperScorpius (US), and 16-20 Myr for Upper Centaurus Lupus (UCL) and forLower Centaurus Crux (LCC). Thus, our results do not confirm that UCL isolder than the LCC association. Based on these results and theuncertainties associated with the age determination, we cannot say thatthere is indeed a difference in the age of the two populations. Weanalyze the different scenarios for the triggering of large-scalestar-formation that have been proposed up to now, and argue that mostprobably we are observing a spiral arm that passes close to the Sun. Thealignment of young stars and molecular clouds and the average velocityof the stars in the opposite direction to the Galactic rotation agreewith the expected behavior of star formation in nearby spiral arms.Tables 1 to 4 are only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/404/913
| 2 Micron Narrowband Adaptive Optics Imaging in the Arches Cluster
Canada-France-Hawaii-Telescope adaptive optics bonnette images throughnarrowband filters in the K band are presented for the Arches cluster.Continuum fluxes, line fluxes, and equivalent widths are derived fromhigh angular resolution images, some nearly diffraction limited, for thewell-known massive stars in the Arches cluster. Images were obtained inthe lines He I 2.06 μm, H I Brγ (2.17 μm), and He II 2.19μm, as well as continuum positions at 2.03, 2.14, and 2.26 μm. Inaddition, fluxes are presented for H I Pα (1.87 μm) and anearby continuum position (1.90 μm) from Hubble Space Telescopearchival data.2 The 2 μm and Pαdata reveal two new emission-line stars and three fainter candidateemission-line objects. Indications for a spectral change of one objectbetween earlier observations in 1992-1993 and our data from 1999 arefound. The ratio of He II 2.19 μm to Brγ emission exhibits anarrow distribution among the stars, suggesting a narrow evolutionaryspread centered predominantly on spectral types O4 If or Wolf-Rayetstars of the WN7 subtype. From the approximate spectral types of theidentified emission-line stars and comparisons with evolutionary modelswe infer a cluster age between ~2 and 4.5 Myr.
| A spectroscopic survey for lambda Bootis stars. II. The observational data
lambda Bootis stars comprise only a small number of all A-type stars andare characterized as nonmagnetic, Population i, late B to early F-typedwarfs which show significant underabundances of metals whereas thelight elements (C, N, O and S) are almost normal abundant compared tothe Sun. In the second paper on a spectroscopic survey for lambda Bootisstars, we present the spectral classifications of all program starsobserved. These stars were selected on the basis of their Strömgrenuvbybeta colors as lambda Bootis candidates. In total, 708 objects insix open clusters, the Orion OB1 association and the Galactic field wereclassified. In addition, 9 serendipity non-candidates in the vicinity ofour program stars as well as 15 Guide Star Catalogue stars were observedresulting in a total of 732 classified stars. The 15 objects from theGuide Star Catalogue are part of a program for the classification ofapparent variable stars from the Fine Guidance Sensors of the HubbleSpace Telescope. A grid of 105 MK standard as well as ``pathological''stars guarantees a precise classification. A comparison of our spectralclassification with the extensive work of Abt & Morrell(\cite{Abt95}) shows no significant differences. The derived types are0.23 +/- 0.09 (rms error per measurement) subclasses later and 0.30 +/-0.08 luminosity classes more luminous than those of Abt & Morrell(\cite{Abt95}) based on a sample of 160 objects in common. The estimatederrors of the means are +/- 0.1 subclasses. The characteristics of oursample are discussed in respect to the distribution on the sky, apparentvisual magnitudes and Strömgren uvbybeta colors. Based onobservations from the Observatoire de Haute-Provence, OsservatorioAstronomico di Padova-Asiago, Observatório do Pico dosDias-LNA/CNPq/MCT, Chews Ridge Observatory (MIRA) and University ofToronto Southern Observatory (Las Campanas).
| Near-Infrared Coronagraphic Imaging of the Circumstellar Disk around TW Hydrae
We present ground-based near-infrared (H-band) imaging of thecircumstellar disk around the nearby classical T Tauri star TW Hydrae.The scattered-light image shows a face-on disk with a radius of 4"(corresponding to 225 AU) and a morphology that agrees with recentimages from the Hubble Space Telescope and the Very Large Array. Thebest-fit power-law for the disk's radial surface brightness profileobeys the law r-3.3+/-0.3. We use our image and publishedcontinuum flux densities to derive properties of the disk with a simplemodel of emission from a flat disk. The best-fit values for disk massand inner radius are 0.03 Msolar and 0.3 AU, respectively;the best-fit values for the temperature, density, and grain opacitypower-law exponents (q, p, and ?) are 0.7, 1.3, and 0.9,respectively. These properties are similar to those of disks aroundclassical T Tauri stars located in more distant molecular clouds.Because of TW Hydrae's nearby location and pole-on orientation, it is auniquely favorable object for future studies of radial disk structure atthe classical T Tauri stage.
| Towards a fundamental calibration of stellar parameters of A, F, G, K dwarfs and giants
I report on the implementation of the empirical surface brightnesstechnique using the near-infrared Johnson broadband { (V-K)} colour assuitable sampling observable aimed at providing accurate effectivetemperatures of 537 dwarfs and giants of A-F-G-K spectral-type selectedfor a flux calibration of the Infrared Space Observatory (ISO). Thesurface brightness-colour correlation is carefully calibrated using aset of high-precision angular diameters measured by moderninterferometry techniques. The stellar sizes predicted by thiscorrelation are then combined with the bolometric flux measurementsavailable for a subset of 327 ISO standard stars in order to determineone-dimensional { (T, V-K)} temperature scales of dwarfs and giants. Theresulting very tight relationships show an intrinsic scatter induced byobservational photometry and bolometric flux measurements well below thetarget accuracy of +/- 1 % required for temperature determinations ofthe ISO standards. Major improvements related to the actual directcalibration are the high-precision broadband { K} magnitudes obtainedfor this purpose and the use of Hipparcos parallaxes for dereddeningphotometric data. The temperature scale of F-G-K dwarfs shows thesmallest random errors closely consistent with those affecting theobservational photometry alone, indicating a negligible contributionfrom the component due to the bolometric flux measurements despite thewide range in metallicity for these stars. A more detailed analysisusing a subset of selected dwarfs with large metallicity gradientsstrongly supports the actual bolometric fluxes as being practicallyunaffected by the metallicity of field stars, in contrast with recentresults claiming somewhat significant effects. The temperature scale ofF-G-K giants is affected by random errors much larger than those ofdwarfs, indicating that most of the relevant component of the scattercomes from the bolometric flux measurements. Since the giants have smallmetallicities, only gravity effects become likely responsible for theincreased level of scatter. The empirical stellar temperatures withsmall model-dependent corrections are compared with the semiempiricaldata by the Infrared Flux Method (IRFM) using the large sample of 327comparison stars. One major achievement is that all empirical andsemiempirical temperature estimates of F-G-K giants and dwarfs are foundto be closely consistent between each other to within +/- 1 %. However,there is also evidence for somewhat significant differential effects.These include an average systematic shift of (2.33 +/- 0.13) % affectingthe A-type stars, the semiempirical estimates being too low by thisamount, and an additional component of scatter as significant as +/- 1 %affecting all the comparison stars. The systematic effect confirms theresults from other investigations and indicates that previousdiscrepancies in applying the IRFM to A-type stars are not yet removedby using new LTE line-blanketed model atmospheres along with the updatedabsolute flux calibration, whereas the additional random component isfound to disappear in a broadband version of the IRFM using an infraredreference flux derived from wide rather than narrow band photometricdata. Table 1 and 2 are only available in the electronic form of thispaper
| Determination of the temperatures of selected ISO flux calibration stars using the Infrared Flux Method
Effective temperatures for 420 stars with spectral types between A0 andK3, and luminosity classes between II and V, selected for a fluxcalibration of the Infrared Space Observatory, ISO, have been determinedusing the Infrared Flux Method (IRFM). The determinations are based onnarrow and wide band photometric data obtained for this purpose, andtake into account previously published narrow-band measures oftemperature. Regression coefficients are given for relations between thedetermined temperatures and the photometric parameters (B2-V1), (b-y)and (B-V), corrected for interstellar extinction through use ofHipparcos parallaxes. A correction for the effect of metallicity on thedetermination of integrated flux is proposed. The importance of aknowledge of metallicity in the representation of derived temperaturesfor Class V, IV and III stars by empirical functions is discussed andformulae given. An estimate is given for the probable error of eachtemperature determination. Based on data from the ESA HipparcosAstrometry Satellite.
| The obscuration to the nucleus of IC 5063.
Not Available
| A homogeneous catalog of new UBV and H-beta photometry of B- and A-type stars in and around the Scorpius-Centaurus OB association
B- and A-type stars in and near the Sco-Cen OB association areinvestigated with UBV and H-beta photometry to acquire data relevant tothe luminosity function of Sco-Cen. The measurements generally consistof two 10-s integrations of U, B, V, (W, N) filters, and theobservations are corrected iteratively for atmospheric extinction andinstrumental response. The data presented give the mean V magnitude,mean B-V, mean U-B, and the estimated uncertainties for these values.The catalog provides a homogeneous catalog of data for a large fieldwith stellar objects delineating membership to the association Sco-Cenand that affect the luminosity function of the aggregate.
| Walraven photometry of nearby southern OB associations
Homogeneous Walraven (VBLUW) photometry is presented for 5260 stars inthe regions of five nearby southern OB associations: Scorpio Centaurus(Sco OB2), Orion OB1, Canis Major OB1, Monoceros OB1, and Scutum OB2.Derived V and (B - V) in the Johnson system are included.
| Southern JHKL standards
The basis for the current SAAO standard photometric system at JHKL isgiven. This depends on an extensive investigation involving 230 starsdistributed around the sky. The accuracy is estimated at + or - 0.02 magfor J, H and K and + or - 0.05 mag for L.
| Physical parameters of stars in the Scorpio-Centaurus OB association
Walraven photometry is presented of established and probable members ofthe Scorpio-Centaurus OB association. For each star, effectivetemperature and surface gravity are derived using Kurucz (1979)atmosphere models. From the Straizys and Kuriliene (1981) tables,absolute magnitudes are calculated. Distance moduli and visualextinctions are determined for all stars. From a comparison of theHR-diagrams of the stars in each subgroup with theoretical isochrones,the ages of the three subgroups are derived. The distances to the threesubgroups are shown to be different; there is a general trend (alsowithin each subgroup) for the distances to be larger at higher galacticlongitudes. The visual extinction in the youngest subgroupUpper-Scorpius, is well correlated with the IRAS 100-micron map. Thedistance toward the Ophiuchus dark clouds is found to be 125 pc, basedon the photometric distances to the stars. Most of the early-type starsin Upper-Scorpius are located at the far side of the dark clouds.
| Possible new members of a subgroup of the Scorpio-Centaurus association.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1972AJ.....77..474G&db_key=AST
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| קבוצת-כוכבים: | קנטאור |
| התרוממות ימנית: | 14h47m46.94s |
| סירוב: | -39°55'35.1" |
| גודל גלוי: | 6.91 |
| מרחק: | 196.85 פארסק |
| תנועה נכונה: | -33 |
| תנועה נכונה: | -10.7 |
| B-T magnitude: | 6.944 |
| V-T magnitude: | 6.913 |
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